a humped blade serves three purposes that I am currently aware of. One is to help protect the spindle bolt by mere the fact that it is recessed in relationship to the cutting edges/height. If they'll clear, so will the spindle bolt (as in going on or off the trailer or over a root, shallow small stumpe etc). Also, a spindle designed to run flat blades has to be longer to keep the blade in the lower part of the deck where most machines run their blades.
The main reason though is to help eliminate the drag on the grass surface by the entire length of the blade which can only reduce power, and cause extra wear to the spindle bearings.
Last edited by Ridin' Green; 06-02-2012 at 02:50 PM.